Recording liquid

ABSTRACT

In a recording liquid comprising, as essential components, a colorant in an amount necessary to image formation, water, an a water-miscible organic solvent, said recording liquid is characterized in that the total number of colonies in the Ames test thereof is not more than four times that of the control test using sterilized water.

This is a continuation of application Ser. No. 763,878, filed Aug. 8,1985, (now U.S. Pat. No. 4,655,835, issued April 1 1987) and is relatedto application Ser. No. 761,502, filed August 1, 1985 (now U.S. Pat. No.4,655,834, issued April 7, 1987), respectively a continuation and adivision of application Ser. No. 490,732, filed May 2, 1983, nowabandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a recording liquid suitable for ink-jetrecording by ejecting droplets through orifices of a recording head aswell as for recording by use of usual writing tools.

2. Description of the Prior Art

Ink-jet recording generates less and permits high speed recording onplain paper without requiring any particular fixing treatment, so thatvarious types of ink-jet systems are investigated energetically.

Recording liquid for use in the ink-jet system is demanded to fulfillthe following requirements: (1) its physical properties such asviscosity and surface tension are within proper respective ranges; (2)it does not clog fine orifices for discharging; (3) it gives recordingimages with clear color and with sufficiently high optical density; and(4) it does not make any change in its physical properties or depositsolid matter during storage. In addition, the following properties arerequested: (5) recording can be performed on any of recording media suchas paper and the like; (6) it can be fixed on recording media at highrates; (7) it gives images which are excellent in resistance to water,solvent (in particular, alcohol resistance), light, and abrasion andhave a high degree of resolution; and (8) it is innocuous to human body.

On the other hand, when used for recording by means of conventionalwriting tools such as fountain pens, felt pens, and the like, recordingliquid is requested to have similar properties as in the case of ink-jetrecording, in particular to be excellent in solution stability (theabove requirements (2), (4) and such) since the supplement of recordingliquid to pen points are accomplished by making use of capillarity.Accordingly, a recording liquid which fulfills the requirements inink-jet applications can also be used in conventional writing toolapplications.

Recording liquid used for ink-jet recording is composed basically of adye for recording purposes and its solvent. The above noted propertiesof recording liquid are much affected by properties proper to theingredient dye and by the solvent composition. It is therefore veryimportant in the art to select a dye and a solvent composition so as toprovide the recording liquid with the above properties requested.

The solubility of the ingredient colorant in vehicle materials is ofgreat importance, that is, a sufficient solubility of the colorant inwater and also in a water-miscible organic solvent such as a wettingagent is essential for the recording liquid to maintain a goodanti-clogging property and a high storage stability.

SUMMARY OF THE INVENTION

An object of this invention is to provide a recording liquid for ink-jetrecording and writing by use of writing tools which is excellent in thesolubility of its ingredient colorant and maintains a high solutionstability during storage.

Another object of this invention is to provide a recording liquid whichis harmless to human body, does not clog the discharging orifice whenused for ink-jet recording and can be smoothly supplied to pen pointswhen used for writing by means of writing pens.

Thus, this invention provide a recording liquid comprising, as essentialcomponents, a colorant in an amount necessary to image formation, water,and a water-miscible organic solvent, said recording liquid beingcharacterized in that the total number of colonies in the Ames test ofthe recording liquid is not more than four times that of the controltest using sterilized water.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

It has been found that an intimate relationship exists between theresult of the Ames test (a mutuation activity test generally known as amethod of evaluating toxicity) of recording liquid and the storagesolution stability thereof, and that the storage solution stabilityrapidly falls when the Ames test value exceeds a specific value eventhough this specific value is not problematic in toxicity.

The Ames test in this invention is conducted in accordance with thefollowing procedure:

The strain used in the Ames test is a histidine-requirement (His⁻)strain incapable of synthesizing histidine, belonging to the genusSalmonella typhimurium. The His⁻ strain, when placed under the action ofa toxic sample, reverts to a histidine-non-requirement (His⁺) strain(revertant to histidine prototrophy). The mutagenesis of the test sampleis determined by counting the number of colonies of this revertant His⁺strain. At present, TA1535, TA1537, TA100 and TA98 among the strainsused for the Ames test are generally recommended however, a goodcorrelation is observed between the test value and the solutionstability of recording liquid when TA98 is used. Consequently, TA98 isused for the Ames test in this invention.

In the Ames test, two tests are generally made in combination, one beinga direct test in which the test sample is allowed to act as such onstrain bodies and the other being a metabolism activation test in whicha drug metabolism activating enzyme (so-called S-9 Mix) obtained fromthe liver of rats or the like is incorporated for the purpose ofapproximating the drug metabolizing system of the microorganism to thatof the mammal; but the former direct test only is carried out in thisinvention by reason that results of the direct test generally indicate amore clear distinction between the sample and control and a bettercorrelation to the storage solution stability.

Referring to the Ames test procedure, detailed description has beengiven, for example, in Mutat. Res., 31, 347(1975). Accordingly, theprocedure is briefly described below.

The bacterial tester strain-containing liquid is prepared by subjectinga medium containing a nutrient broth (8 g/l) and sodium chloride (5 g/l)to a high-pressure steam sterilization, inoculating the medium withTA98, and shaking the medium at 37° C. for 16 hours to grow the strain.

A suitable agar plate medium is prepared by high-pressure steamsterilization of the composition:

    ______________________________________                                        Distilled water           900    ml                                           Volgel-Bonner's minimal medium liquor                                                                   100    ml                                           Glucose (2.0%)            20     g                                            Agar (1.5%)               15     g                                            ______________________________________                                    

and taking in part about 25 ml of the sterilized composition in asterilized Petri dish to solidify it. The Volgel-Bonner's minimal mediumliquor is prepared by dissolving 2g of MgSo₄.7H₂ O, 20 g of citric acidmonohydrate, 100 g of dipotassium hydrogenphosphate, and 35 g of NaNH₄HPO₄.4H₂ O in distilled water, and adjusting the total volume to 1000ml.

Using the bacterial tester strain-containing liquid and the agar medium,the Ames mutation activity test of the sample is conducted according toa so-called pre-incubation method as follows:

The above bacterial tester strain-containing liquid (0.1 ml), thesolution (0.1 ml) of sample to be tested or the control liquid(distillated and sterilized water) (0.1 ml), and a 100 mM sodiumphosphate buffer solution (pH7.4, 0.5 ml) are added to 2 ml of a softagar solution containing 0.7% by weight of agar, 0.6% by weight of NaCl0.05 mM of L-hystidine, and 0.05 mM of biotin which is put in asterilized small test tube kept at 45° C. The liquid is well mixed andthen shaken in an incubator at 37° C. for about 20 minutes to grow thestrain. The liquid in the test tube is poured onto the agar platemedium, and the Petri dish, after solidification of the soft agar, isplaced in the dark at 37° C. for 48 hours, and the number of thecolonies (revertants to histidine prototrophy) is counted.

When the number of the colonies determined in the Ames test thus carriedout is not more than four times that determined in the control Amestest, the sample recording liquid is excellent in storage solutionstability and of course intoxic to human body. Preferably, the number ofthe colonies for the recording liquid is not more than triple that forthe control.

The ingredient colorant in the recording liquid of this invention playsa role as the coloring component of recording liquid, and is categorizedgenerally as a dye or pigment. The colorant content in the recordingliquid is in the range necessary to image formation. This content,though dependent upon the water content, the kinds and contents of thewater-miscible organic solvents and the like contained, and requestedproperties of recording liquid, is required in the range of 1 to 20% byweight, and is desirably in the range of 1 to 10%, preferably 1-6%, byweight.

The recording liquid of this invention contains water and awater-miscible organic solvents as essential components for dissolvingthe component colorant.

Water-miscible solvents for this purpose include, for example, C₁ -C₄alkyl alcohols such as methanol, ethanol, n-propanol, isopropanol,n-butanol, sec-butanol, tert-butanol, and isobutanol; amides such asdimethylformamide, dimethylacetamide, and the like; ketones orketo-alcohols such as acetone, diacetone alcohol, and the like; etherssuch as tetrahydrofuran, dioxane, and the like; polyalkylene glycolssuch as polyethylene glycol, polypropylene glycol, and the like;alkylene glycol having 2-6 carbon atoms in the alkylene group such asethylene glycohol, propylene glycol, butylene glycol, triethyleneglycol, 1, 2, 6-hexanetriol, thiodiglycol, hexylene glycol, diethyleneglycol, and the like; glycerol; lower alkyl ethers of polyhydricalcohols such as ethylene glycol methyl ether, diethylene glycol methyl(or ethyl) ether, triethylene glycol monomethyl (or monoethyl) ether,and the like; and nitrogen-containing heterocyclic ketones such asN-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, and the like.

Among these various water-miscible organic solvents, polyhydric alcoholssuch as diethylene glycol and lower alkyl ethers of polyhydric alcoholssuch as triethylene glycol monomethyl (or monoethyl) ether arepreferable. Polyhydric alcohols are particularly preferable because theyhave a great wetting effect for preventing the clogging of thedischarging orifices due to the deposition of the colorant byevaporation of the water contained in the recording liquid.Nitrogen-containing heterocyclic ketones such as N-methyl-2-pyrrolydoneand the like are also taken as an example of particularly preferablesolvents because they are much effective as a so-called solubilizer forimproving markedly the solubility of the colorant in the solvent.

The content of the water-miscible organic solvent in the recordingliquid is generally 5-95%, preferably 10-80%, and more preferably20-50%, by weight based on the total weight of recording liquid.

The water content, though dependent upon the kind and content of thesolvent and desired properties of the recording liquid, is selected froma wide range of generally 10-90%, preferably 10-70%, and more preferably20-70%, by weight based on the total weight of recording liquid.

The recording liquid of this invention formulated from these componentsis excellent as it is, having balanced recording characteristics(responsiveness to signals, stability of droplet formation, dischargestability, long-hour continuous recordability, and discharge stabilityafter a long period of rest time), storage stability, solution stabilityof the colorant, fixability onto recording media such as paper and thelike, and light resistance, weather resistance, water resistance, andalcohol resistance, of the image formed. For further improvements ofthese characteristics, various additives hitherto known may beincorporated.

Such additives include, for example, viscosity regulators such aspoly(vinyl alcohol), celluloses, and other water-soluble resins; variouscationic, anionic, and nonionic surfactants; surface tension regulatorssuch as diethanolamine, triethanolamine, and the like; and pH regulatorsemploying buffers.

In order to prepare a recording liquid for use in the method ofrecording by electrical charging of recording liquid droplets, aresistivity regulator is incorporated such as an inorganic salt, e.g.lithium chloride, ammonium chloride, or sodium chloride. Further, ureaor thiourea is suitably used for improving the water retention atdischarging tips. In the case of a recording liquid to be discharged bythe action of thermal energy, its thermal properties (e.g. specificheat, thermal expansion coefficient, heat conductivity, etc.) areregulated in certain cases.

Although suitable in particular for ink-jet recording applications, therecording liquid of this invention can also be used favorably forwriting applications by means of conventional writing tools such asfountain pens, felt pens, and the like.

This invention will be illustrated in more detail with reference to thefollowing preparation examples, examples, and comparative examples:

PREPARATION EXAMPLE 1 (Reaction 1)

In a 4-liter 3-necked flask was put 0.28 mole of2-naphthylamine-8-sulfonic acid and was gradually added dropwise 0.1 Naq. NaOH so as not to raise the temperature over 40° C. until the pHreached 7. Then, 600 g of ice was added, and after the temperaturedropped to 10° C., reaction was conducted by adding 100 ml of 37% conc.HCl and 85 ml of 30% aq. NaNO₂, with stirring at 18° C. for 2 hours. Onthe other hand, 0.34 mole of m-toluidine was put in a 5-liter 3-neckedflask, and then 500 ml of distilled water and 50 ml of 37% conc. HClwere added. The mixture was heated to 50° C. to dissolve the toluidine,then was cooled to 30° C. with an ice-cold water bath, and reaction wasconducted by adding the reaction mixture prepared in the 2-liter3-necked flask, at 20° C. for 30 minutes. Then, 500 ml of 20% aq. sodiumacetate was added and the mixture was stirred at room temperature forabout 20 hours. Then, 125 ml of 37% conc. HCl was added to acidify themixture, the resulting mixture was filtered by using a qualitativefilter paper, and the filter cake was dried in a vacuum desicator.

(Reaction 2)

The product obtained by reaction 1 was all put in a 2-liter beaker, oneliter of distilled water and 60 ml of 40% aq. NaOH were added, themixture was heated at 40°-50° C. to dissolve the product, and 85 ml of30% aq. NaNO₂ was added. On the other hand, 180 ml of 37% conc. HCl and600 g of ice were put in a 4-liter 3-necked flask, the formerly preparedcontent in the beaker was gradually added, and the mixture was stirredfor 1 hour. The reaction product was filtered by using a qualitativefilter paper, the filter paste was put in a 2-liter beaker, and 300 g ofice and 500 ml of distilled water were added to dissolve the productwith stirring. Besides this, 0.32 mole of1-amino-2-ethoxynatphthalene-6-sulfonic acid was put in a 4-liter,3-necked flask, one liter of distilled water and 0.1 N aq. NaOH wereadded dropwise up to pH 7, and the sulfonic acid was completelydissolved at 40° C. The solution was cooled to 20°-25° C., the abovesolution of filter paste was added dropwise, and further 450 ml of 20%aq. sodium acetate was added. After 7-hour stirring, 37.5 g of Na₂ CO₃was added, and the mixture was heated for 1-2 hours up to 60° C. Aboutone liter of 10% a. NaC1 was added for salting out, the separated matterwas filtered by using a qualitative filter paper, and the filter cakewas dried in a vacuum desiccator.

(Reaction 3)

The product obtained by reaction 2 was all put in a 2-liter 3-neckedflask, 600 ml of distilled water and 500 ml of 50% acetic acid wereadded, and the mixture was stirred so that the temperature would notexceed 30° C. After cooling below 20° C., 100 ml of 30% aq. NaOH wasadded, and the mixture was stirred for 7 hours to prepare a liquid(designated as liquid A).

On the other hand, 0.28 mole of H acid was put in a 2-liter 3-neckedflask, 500 ml of distilled water was added to dissolve it, and 32 ml of40% aq. NaOH and 17 g of Na₂ CO₃ were further added. After thetemperature was raised up to 70° C., 50 g of acetic anhydride was added,and the mixture was stirred until it cooled to room temperature. Theresulting solution was added to a mixture of 1.5 liters of pyridine and2 Kg of ice contained in a 10-liter 3-necked flask and was thoroughlymixed. Further, liquid A was added and mixed at 60° C. for 1 hours,about 2 liters of 10% aq. NaCl was added for salting out, and theseparated matter was filtered by using a qualitative filter paper togive a filter cake.

(Purification)

The filter cake (10 g) and methyl Cellosolve (300 ml) were mixed bystirring in a beaker for about 3 hours to dissolve the cake. Thesolution was filtered with a qualitative filter paper No. 2 (mfd. byToyo Roshi Co., Ltd.), and the filtrate was evaporated to dryness,giving a dye (designated as dye A).

PREPARATION EXAMPLE 2

Dye B was prepared by repeating the procedure of Preparation Example 1except that the same molar quantity of naphthionic acid was used inplace of 3-naphthylamine-8-sulfonic acid in reaction 1 and the samemolar quantity PR acid was used in place of H acid in reaction 3.

PREPARATION EXAMPLE 3

Dye C was prepared by repeating the procedure of Preparation Example 1except that the same molar quantity of 1-naphthylamine-5-sulfonic acidwas used in place of 2-naphthylamine-8-sulfonic acid in reaction 1.

PREPARATION EXAMPLE 4

Dye D was prepared by repeating the procedure of Preparation Example 1except that the same molar quantity of Cleve's acid-7 was used in placeof 2-naphthylamine-8-sulfonic acid in reaction 1 and the same molarquantity of K acid was used in place of H acid in reaction 3.

PREPARATION EXAMPLE 5

In a 4-liter 3-necked flask was put 0.25 mole of sulfanilic acidtogether with 800 ml of distilled water and was dissolved completely at70° C. Then, 80 ml of 37% conc. HCl and 500 g of ice were added, andwhen the liquid temperature dropped to 18°-20° C., 25 g of 23% aq. NaNO₂was added and mixed for 1 hour. Then, 0.28 mole of 1,7-Cleve's acid inpaste form and further 450 ml of 20% aq. sodium acetate were added, andthe mixture was stirred at 18° C. for 10 hours. After 80 ml of 40% aq.NaOH was added, the temperature was raised to 25° C. and 900 g of NaCland 30 g of 23% aq. NaNO₂ were added. Further, 250 ml of 37% conc. HClwas added, and the reaction mixture was filtered with a qualitativefilter paper. The filter paste obtained was mixed with 300 ml ofdistilled water and 300 g of ice.

On the other hand, 0.25 mole of RR acid togther with 500 ml of distilledwater was put in a 4-liter 3-necked flask and was completely dissolvedby adding 0.1 N aq. NaOH up to pH 7. After cooling of the mixture to 0°C. by adding 1 Kg of ice, pyridine and then the formerly obtained pastewere added, and the mixture was stirred for 10 hours. A large amount ofNaCl was added for salting out, and, after stirring 2 hours, the mixturewas filtered with a qualitative filter paper. The resulting filter cakewas purified in the same manner as in "Purification" of PreparationExample 1, to give a dye (dye E).

PREPARATION EXAMPLE 6

A mixture of 400 parts (hereinafter , all "parts" are by weight) ofchlorosulfonic acid and 50 parts of copper phthalocyanine was heatedwith stirring at 125°-130° C. for 4 hours. After cooling on standing,the product mixture was gradually added dropwise into a mixture of 500parts of water and 200 parts of ice. The mixture was filtered, and thefilter cake was washed with cold water. The filter cake was neutralizedby adding it to a 5% solution of equivalent amount of NaOH, the solventwas evaporated, the residue was dissolved in Cellosolve, the solutionwas filtered with a qualitative filter paper No. 2 (mfd. by ToyoKagakusangyo Co., Ltd.), and the solvent was evaporated from thefiltrate. Thus, a sodium salt of copper phthalocyanine having sulfosubstituents was obtained (dye F).

PREPARATION EXAMPLE 7

A mixture of 150 parts of 4-sulfophthalic acid, 135 parts of urea, 24parts of cupric chloride, and 0.5 parts of ammonium molybdate wasreacted by stirring together with 300 parts of trichlorobenzene at 200°C. for 2 hours. The product mixture was hot-filtered, and the filtercake obtained was treated in the same manner as in "Purification" ofPreparation Example 1, to give a dye (dye G).

EXAMPLES 1-12 AND COMPARATIVE EXAMPLES 1-14

Using dyes obtained in Preparation Examples 1-7 and commercial dyes,recording liquids were prepared respectively according to the followingfour formulations:

    ______________________________________                                        Formulation I                                                                 Glycerol            30      parts by weight                                   N--Methyl-2-pyrrolidone                                                                           10      "                                                 Distilled water     60      "                                                 Dye                 1.5-4   "                                                 Formulation II                                                                Ethylene glycol     40      parts by weight                                   N--Methyl-2-pyrrolidone                                                                           15      "                                                 Distilled water     45      "                                                 Dye                 1.5-3   "                                                 Formulation III                                                               Triethylene glycol  20      parts by weight                                   monomethyl ether                                                              Glycerol            10      "                                                 N--Methyl-2-pyrrolidone                                                                           10      "                                                 Distilled water     60      "                                                 Dye                 0.8-4   "                                                 Formulation IV                                                                Polyethylene glycol (M.W. 300)                                                                    15      part by weight                                    Diethylene glycol   15      "                                                 1,3-Dimethyl-2-imidazolidinone                                                                    10      "                                                 Distilled water     60      "                                                 Dye                 0.8-2.5 "                                                 ______________________________________                                    

Components of each formulation were thoroughly mixed together in avessel to form a solution, which was then pressure-filtered through aTeflon filter of 1μ pore size. The filtrate was degassed in vacuo to bemade up into recording liquid.

Compositions of the recording liquids prepared are summarized inTable 1. The Ames test, solution stability test, and ink-jet recordingperformance test were conducted on these recording liquids. The resultsare also shown in Table 1. The above tests and the evaluation of testresults were made as follows:

(Ames test)

In accordance with the procedure described above, TA98 was cultivated inthe presence of the sample recording liquid in the dark at 37° C. for 48hours and the number of revertant colonies was counted. This number wascompared with that of the control test. (Solution stability test)

The sample recording liquid was allowed to stand in a sealed glasscontainer at 60° C. for 6 months, and thereafter was pressure-filteredthrough a Teflon filter of 1μ pore size to examine whether a precipitateis present or absent and the amount of the precipitate if present. Theevaluation criteria are as follows:

-: No precipitate was found.

+: A very small amount of precipitate was observed on the filter.

++: A relatively large amount of precipitate was observed on the filter.

+++: A precipitate was observed in the glass container.

(Ink-jet recording performance test)

The ink-jet recorder used was provided with an on-demand type ofrecording head which discharges recording liquid through 50μ dia.orifices by the action of piezo oscillators (piezo oscillator drivingvoltage 80 V, its frequency 3 KHz). The sample recording liquid wassupplied to this recorder and allowed to stand for 4 months underenviromental conditions of 20° C. and about 60% R.H. Then, recording wasconducted for about 10 minutes. The evaluation criteria are as follows:

O: Trouble-less recording was possible.

X: Ink discharge often stopped.

XX: Ink was not discharged.

(Image quality test)

Visual examination of image density was made on the letters printed inthe above ink-jet recording test. The evaluation criteria as follows:

O: The letters was sufficient in image density and easy to read.

X: The letters exhibited low image density and was difficult to read.

                                      TABLE 1                                     __________________________________________________________________________           Composition of recording liquid                                                                       Result of Ames test  Ink-jet                          Colorant and                      Ratio of                                                                            Solution                                                                           recording                                                                            Image                     Colorant         Formulation                                                                          Sample                                                                             Control                                                                            sample to                                                                           stability                                                                          performance                                                                          quality                   Concentration                                                                            (wt part)                                                                           No.    liquid                                                                             liquid                                                                             control                                                                             test test   test               __________________________________________________________________________    Example No.                                                                   Example 1                                                                            Dye A      4.0   I       67  64   1.0   -    O      O                  Example 2                                                                            Dye A      2.0   I       68  "    1.0   -    O      O                  Example 3                                                                            Dye B      2.5   IV     243  "    3.8   -    O      O                  Example 4                                                                            Dye C      3.0   II      76  "    1.2   -    O      O                  Example 5                                                                            Dye C      1.5   II      70  "    1.1   -    O      O                  Example 6                                                                            Dye D      3.0   III    134  "    2.1   -    O      O                  Example 7                                                                            Dye E      4.0   III    213  "    3.3   -    O      O                  Example 8                                                                            Dye E      2.0   III    180  "    2.8   -    O      O                  Example 9                                                                            Dye F      3.0   IV      83  "    1.3   -    O      O                  Example 10                                                                           Dye F      1.0   IV      72  "    1.1   -    O      O                  Example 11                                                                           Dye G      2.5   II     104  "    1.6   -    O      O                  Example 12                                                                           Dye G      1.5   IV      73  "    1.1   -    O      O                  Comparative                                                                   Example No.                                                                   Comparative                                                                          C.I. Acid Black 107                                                                      3.0   I      524  64   8.2   +++  XX     --                 Example 1                                                                     Comparative                                                                          C.I. Acid Black 107                                                                      1.5   I      480  "    7.5   +++  XX     --                 Example 2                                                                     Comparative                                                                          C.I. Acid Black                                                                          2.0   II     391  "    6.1   ++   XX     --                 Example 3                                                                            52:1                                                                   Comparative                                                                          C.I. Direct Black 19                                                                     1.5   IV     497  "    7.7   +++  XX     --                 Example 4                                                                     Comparative                                                                          C.I. Direct Blue 236                                                                     1.5   II     322  "    5.0   +    X      O                  Example 5                                                                     Comparative                                                                          C.I. Direct Yellow                                                                       2.0   I      336  "    5.2   +    X      O                  Example 6                                                                            44                                                                     Comparative                                                                          C.I. Acid Yellow 59                                                                      2.0   III    405  "    6.3   ++   XX     --                 Example 7                                                                     Comparative                                                                          C.I, Acid Yellow 59                                                                      0.8   III    369  "    5.7   +    O      X                  Example 8                                                                     Comparative                                                                          C.I. Acid Yellow 114                                                                     1.5   IV     410  "    6.4   ++   XX     --                 Example 9                                                                     Comparative                                                                          C.I. Acid Yellow 161                                                                     1.5   IV     288  "    4.5   +    X      O                  Example 10                                                                    Comparative                                                                          C.I. Acid Red 180                                                                        2.0   I      269  "    4.2   ++   X      O                  Example 11                                                                    Comparative                                                                          C.I. Acid Red 214                                                                        1.5   IV     443  "    6.9   +++  XX     --                 Example 12                                                                    Comparative                                                                          C.I. Acid Red 214                                                                        0.8   IV     358  "    5.6   +    O      X                  Example 13                                                                    Comparative                                                                          C.I. Acid Red 315                                                                        1.5   II     295  "    4.6   ++   XX     --                 Example 14                                                                    __________________________________________________________________________

What we claim is:
 1. A recording liquid comprising a colorant in anamount necessary for image formation, water and a water-miscible organicsolvent, said recording liquid being characterized in that the totalnumber of colonies resulting from an Ames test thereof is not more thanfour times the number in a control test using sterilized water.
 2. Therecording liquid of claim 1, which is characterized in that the totalnumber of colonies in said test is not more than triple that of thecontrol test using sterilized water.
 3. The recording liquid of claim 1,wherein the colorant content is 1-20% by weight.
 4. The recording liquidof claim 1, wherein the content of the water-miscible organic solvent is5-95% by weight.
 5. The recording liquid of claim 1, wherein the watercontent is 10-90% by weight.
 6. A recording liquid suitable for ink-jetrecording comprising, as essential components, a colorant in an amountnecessary for image formation, water and a water-miscible organicsolvent, said recording liquid being characterized in that the totalnumber of colonies resulting from an Ames test thereof is not more thanfour times the number in a control test using sterilized water.
 7. Arecording liquid according to claim 6 characterized in that the totalnumber of colonies in said Ames test is not more than triple that of thecontrol test using sterilized water.
 8. A recording liquid according toclaim 6 wherein the colorant content is 1-20% by weight.
 9. A recordingliquid according to claim 6 wherein the content of the water-miscibleorganic solvent is 5-95% by weight.
 10. A recording liquid according toclaim 6 wherein the water content is 10-90% by weight.
 11. A recordingliquid according to claim 6 wherein the Ames test is carried out usingstrain TA 98 of Salmonella typhimurium.
 12. A recording liquid accordingto claim 7 wherein the Ames test is carried out using strain TA 98 ofSalmonella typhimurium.
 13. A recording liquid comprising a purified dyein an amount sufficient for visible image formation, water and awater-miscible organic solvent as essential components, said recordingliquid being such that the total number of colonies resulting from anAmes test thereof using a Salmonella typhimurium TA 98 bacterial strainis not more than four times that of a control test using sterilizedwater.
 14. The recording liquid of claim 13 wherein the Ames testthereof yields a total number of colonies not more than three times thatof the control test using sterilized water.
 15. The recording liquid ofclaim 13, said liquid employing a colorant in amounts between 1 and 20%by weight based on the weight of the recording liquid.
 16. The recordingliquid of claim 13, said liquid employing a water-miscible organicsolvent in amounts between 5 and 95% by weight based on the weight ofthe recording liquid.
 17. The recording liquid of claim 13, said liquidemploying water in amounts between 10 and 90% by weight based on theweight of the recording liquid.
 18. The recording liquid of claim 13wherein the sterilized Ames test control water is provided by distilledwater.
 19. The recording liquid according to claim 13, includingutilizing at least one nitrogen-containing heterocyclic ketone as saidwater-miscible organic solvent.